Morphia 介绍
Morphia 是一个轻量级的类型安全的 Java 类库，用来将在
MongoDB 和 Java 对象之间进行映射。
@Entity("employees")
class Employee {
@Id ObjectId id; // auto-generated, if not set (see ObjectId)
String firstName, lastName; // value types are automatically persisted
Long salary = null; // only non-null values are stored
@Embedded Address address;
@Reference Employee manager; // refs are stored*, and loaded automatically
@Reference List<Employee> underlings; // interfaces are supported
@Serialized EncryptedReviews; // stored in one binary field
@Property("started") Date startDate; //fields can be renamed
@Property("left")Date endDate;
@Indexed boolean active = false; //fields can be indexed for better performance
@NotSaved string readButNotStored; //fields can read, but not saved
@Transient int notStored; //fields can be ignored (load/save)
transient boolean stored = true; //not @Transient, will be ignored by Serialization/GWT for example.
//Lifecycle methods -- Pre/PostLoad, Pre/PostSave...
@PostLoad void postLoad(DBObject dbObj) { ... }
}